As the demand for faster, smaller electronic products with increased functionality is increased, stacked packaging schemes, such as package-on-package (POP) packaging, have become increasingly popular. The stacking of different semiconductor packages using stacked packages typically reduces the required footprint size for a semiconductor package in an electronic product. Furthermore, stacked packages can provide a modular solution for constructing electronic devices by permitting different combinations of stacked semiconductor packages using only a few semiconductor package footprints.
Many advanced electronic packages and devices typically include analog and digital circuits in the same electronic device or system. In these so-called “mixed-signal” devices, signals are typically susceptible to degradation as the signals traverse the various components of the electronic device. Furthermore, the analog signals are generally susceptible to electromagnetic interference (EMI) and the presence of digital signals in the vicinity of the analog components. This susceptibility generally allows the EMI from the digital circuits to couple directly into the analog sections of the mixed-signal device, generally resulting in noise being introduced into the analog signals.
For example, even though typical CMOS digital devices in a high speed digital circuit generally have a low quiescent current, simultaneous switching noise (SSN, also known as ground bounce) caused by the CMOS circuit switching current, can be a significant source of EMI to the analog section of mixed signal device leading to increased noise. Additionally, some analog signals can be susceptible to EMI caused by high level signals from other analog circuits, particularly those which swing nearly a full supply voltage range, also resulting in increased noise.